Speculators make markets MORE stable, not less. Or perhaps I should rephrase that - they make markets more rational, because when a speculator sees a price he deems "irrational" he can take a financial position in the other direction and profit if he's correct. This incentive encourages people to critically asses the market in question. A market in which speculation was difficult would be a market I'd be less confident in.
Then you are naive because a speculator will aim to maximize profit, not 'be rational'. That means striving to control the market to the detriment of all others, eliminate competitors etc. 'People' like Goldman Sachs have been expertly subverting the market for quite a while now (starting with some deregulation in the Reagen era), it's anything but rational now. The result is that the economy and the government are taken financially hostage, if they don't cooperate with the robber barons they simply threaten to let the whole thing collapse.
Otherwise I agree with the rest of your points
The US Dollar is dead and buried and quantitative easing is just the last round of wealth redistribution. There are some long term economic problems with the Bitcoin model that I have no answer for, but it's a helluva lot better than the untouchable vampires controlling the economy now.BTW, the fundamental problem is uncontrolled greed in human nature IMHO, not decentralization.
You just can't argue with nitwits like this. It's competition between rival speculators that produces stability. Buying low and selling high keeps the price in the middle.